Positive Electrode Active Material for Lithium Secondary Battery

ABSTRACT

Provided is a novel positive electrode active material which can effectively suppress the quantity of gas generated by the reaction with an electrolytic solution. Proposed is a positive electrode active material for a lithium secondary battery including positive electrode active material particles obtained by equipping the entire surface or a part of a surface of lithium manganese-containing composite oxide particles (also referred to as the “core particles”) operating at a charging voltage in a region exceeding 4.3 V in a metal Li reference potential with a layer A containing at least titanium (Ti), aluminum (Al), zirconium (Zr), or two or more kinds of these.

TECHNICAL FIELD

The present invention relates to a positive active material for alithium secondary battery which can be suitably used as a positiveelectrode active material of a lithium secondary battery.

BACKGROUND ART

Lithium secondary batteries have characteristics that the energy densityis high, its lifespan is long, and the like. Hence, lithium secondarybatteries are widely used as a power source for home appliances such asa video camera, portable electronic devices such as a notebook computerand a mobile phone, and electric tools such as power tools, and theyhave also been recently applied to a large-sized battery that is mountedin an electric vehicle (EV) or a hybrid electric vehicle (HEV).

Lithium secondary batteries are a secondary battery having a structurein which lithium dissolves out from the positive electrode as an ion,moves to the negative electrode, and is absorbed therein at the time ofcharge and the lithium ion conversely returns from the negativeelectrode to the positive electrode at the time of discharge, and thehigh energy density thereof is known to be due to the potential of thepositive electrode material.

As the positive electrode active material of the lithium secondarybattery of this kind, a spinel-type lithium manganese-containingcomposite oxide having a manganese-based spinel structure (Fd-3m) suchas LiMn₂O₄ and LiNi_(0.5)Mn_(1.5)O₄ is known in addition to a lithiumtransition metal oxide having a layer structure such as LiCoO₂, LiNiO₂,and LiMnO₂.

The spinel-type lithium manganese-containing composite oxide hasattracted attention as the next generation positive electrode activematerial for a large-sized battery of an electric vehicle (EV), a hybridelectric vehicle (HEV), or the like since it is non-toxic and safe, hasnature to be strong to overcharge, and the raw material price of whichis inexpensive. In addition, the spinel-type lithium transition metaloxide (LMO) capable of three-dimensionally inserting and releasing a Liion exhibits excellent output characteristics compared to a lithiumtransition metal oxide having a layer structure such as LiCoO₂, and thusit is expected to be used in an application requiring excellent outputcharacteristics such as an EV battery and a HEV battery.

In recent years, it has been known to have an operating potential ofabout 5 V by substituting a part of the Mn sites in LiMn₂O₄ with othermetals (Cr, Co, Ni, Fe, Cu, and the like), and at present, thedevelopment of manganese-based spinel-type lithium transition metaloxide having an operating potential of 4.5 V or more (5 V-class) isbeing actively carried out.

For example, a spinel-type lithium manganese composite oxide positiveelectrode active material having a high capacity obtained by addingchromium as the essential additive component and further adding nickelor cobalt to a spinel-type lithium manganese composite oxide isdisclosed as a positive electrode active material of a lithium secondarybattery having an electromotive force of a 5 V-class in Patent Document1.

A crystal LiMn_(2−y−z)Ni_(y)M_(z)O₄ (where, M: at least one kindselected from the group consisting of Fe, Co, Ti, V, Mg, Zn, Ga, Nb, Mo,and Cu, 0.25≦y≦0.6, and 0≦z≦0.1) of a spinel structure which conductscharge and discharge at a potential of 4.5 V or more with respect to theLi metal is disclosed in Patent Document 2.

A spinel-type lithium manganese composite oxide represented byLi_(a)(M_(x)Mn_(2−x−y)A_(y))O₄ (in Formula, 0.4<x, 0<y, x+y<2, and0<a<1.2. M includes one or more kinds of metal elements which areselected from the group consisting of Ni, Co, Fe, Cr, and Cu and atleast include Ni. A includes at least one kind of metal element selectedfrom Si or Ti; however, the value of the ratio y of A is 0.1<y in a casein which A includes only Ti) is disclosed as a positive electrodematerial for lithium ion secondary battery having a high energy densityso as to have a high voltage of 4.5 V or more with respect to Li inPatent Document 3.

A lithium nickel manganese composite oxide which has a spinel structureand is represented by Formula (I):Li_(1+x)Ni_(0.5−1/4x−1/4y)Mn_(1.5−3/4x−3/4y)B_(y)O₄ (where, in Formula(I), x and y are to be 0≦x≦0.025 and 0<y≦0.01) and characterized in thata median diameter is from 5 to 20 μm, a coefficient of particle sizevariation is from 2.0 to 3.5%, and a BET specific surface area is from0.30 to 1.30 m/g is disclosed as a positive electrode active materialhaving a high capacity density as both of the tap density of thepositive electrode active material and the initial discharge capacity ofa secondary battery fabricated using the positive electrode activematerial are high in Patent Document 4.

However, a problem that the electrolytic solution is decomposed andgenerate a gas in some cases has been pointed out in the case of using alithium nickel manganese composite oxide having a spinel structure as apositive electrode active material of a lithium secondary battery. Amongthem, the problem is a serious problem to be solved particularly in the(5 V-class) manganese-based spinel-type lithium transition metal oxidehaving an operating potential of 4.5 V or more.

As the cause of such generation of gas, it has been believed that thegas is generated as the impurities contained in the positive electrodeactive material react with the electrolytic solution conventionally, andthus it is proposed a method to remove the water-soluble impurities bywashing them with water.

For example, a method for producing a positive electrode active materialfor secondary battery in which a lithium compound, a manganese compound,and at least one kind of metal or metal compound selected from the groupconsisting of Ni, Al, Co, Fe, Mg, and Ca are mixed and calcined toobtain lithium manganese oxide, and the lithium manganese oxide is thenwashed with water, then filtered, and dried to obtain a positiveelectrode active material for secondary battery is proposed in PatentDocument 5.

In addition, a method for removing impurities on the particle surface bywashing the spinel-type lithium transition metal oxide obtained bycalcination is proposed in Patent Documents 6, 7 and 8 as well.

CITATION LIST Patent Document

-   -   Patent Document 1: JP 11-73962 A    -   Patent Document 2: JP 2000-235857 A    -   Patent Document 3: JP 2003-197194 A    -   Patent Document 4: JP 2012-116720 A    -   Patent Document 5: JP 2000-306577 A    -   Patent Document 6: JP 10-340726 A    -   Patent Document 7: JP 10-188979 A    -   Patent Document 8: JP 10-302795 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, there is a case in which it is not possible to effectivelysuppress the gas generation by simply removing the water-solubleimpurities by washing them with water as described above. Particularlyin the case of using a lithium secondary battery at a high operatingpotential, for example, in the case of operating the lithium secondarybattery at a charging voltage in a region exceeding 4.3 V in the metalLi reference potential, it is not possible to effectively suppress thequantity of gas generated by reaction with the electrolytic solution bysimply washing it with water. In addition, there is also a problem thatit is difficult to enhance the charge-discharge cycle ability of thebattery in the case of using the lithium secondary battery at a highoperating potential.

Accordingly, the invention is intended to propose a novel positiveelectrode active material for a lithium secondary battery which caneffectively suppress the quantity of gas generated by the reaction withthe electrolytic solution as well as can improve the charge-dischargecycle ability by taking a different concept from the idea of removingwater-soluble impurities by washing with water with regard to thepositive electrode active material that operates at a charging voltagein a region exceeding 4.3 V.

Means for Solving Problem

The invention proposes a positive electrode active material for alithium secondary battery including positive electrode active materialparticles obtained by equipping the entire surface or a part of thesurface of the lithium manganese-containing composite oxide particles(also referred to as the “core particles”) operating at a chargingvoltage in a region exceeding 4.3 V in the metal Li reference potentialwith a layer (referred to as the “layer A”) containing at least titanium(Ti), aluminum (Al), zirconium (Zr), or two or more kinds of these.

EFFECT OF THE INVENTION

In the positive electrode active material for a lithium secondarybattery proposed by the invention, the entire surface or a part of thesurface of the lithium manganese-containing composite oxide particles(core particles) is provided with a layer A containing at least titanium(Ti), aluminum (Al), zirconium (Zr), or two or more kinds of these, andthus it is possible to suppress the reaction between the lithiummanganese-containing composite oxide particles and the electrolyticsolution, it is possible to improve the charge-discharge cycle ability,and also it is possible to maintain the battery capacity even though thecharge and discharge is repeated, and thus it is possible to effectivelysuppress the quantity of gas generated by the reaction with theelectrolytic solution. Consequently, the positive electrode activematerial for secondary battery proposed by the invention can be suitablyused as the positive electrode active material of various kinds oflithium batteries.

MODE(S) FOR CARRYING OUT THE INVENTION

Next, the invention will be described based on the embodiments forcarrying out the invention. However, the invention is not limited to theembodiments to be described below.

<Present Positive Electrode Active Material>

The positive electrode active material for secondary battery accordingto an example of the present embodiment (hereinafter, referred to as the“present positive electrode active material”) is a positive electrodeactive material for a lithium secondary battery which contains positiveelectrode active material particles (hereinafter, referred to as the“present positive electrode active material particles”) obtained byequipping the entire surface or a part of the surface of lithiummanganese-containing composite oxide particles (also referred to as the“core particles”) with a layer A (referred to as the “layer A”)containing at least titanium (Ti), aluminum (Al), zirconium (Zr), or twoor more kinds of these.

The present positive electrode active material may contain othercomponents as long as it contains the present positive electrode activematerial particles. However, it is preferable that the present positiveelectrode active material particles occupy 70% by mass or more of thepresent positive electrode active material, 90% by mass or more amongthem, and 95% by mass or more (including 100%) among them.

(Core Particles)

The core particles constituting the core portion of the present positiveelectrode active material particles may be a lithiummanganese-containing composite oxide which operates at a chargingvoltage in a region exceeding 4.3 V in the metal Li reference potential.

Since the core particles may be a lithium manganese-containing compositeoxide operating at a charging voltage in a region exceeding 4.3 V, forexample, it may be a lithium manganese-containing composite oxide whichoperates at a charging voltage in a region exceeding 4.5 V and is usedonly in the region or it may be a lithium manganese-containing compositeoxide which operates at a charging voltage of from 3 to 4.5 V and usedin the region.

Hence, the core particles constituting the core portion of the presentpositive electrode active material particles may be a 4 V-class lithiummanganese-containing composite oxide which has an operating potential of3.5 V or more and less than 4.5 V, or it may be a 5 V-class lithiummanganese-containing composite oxide which has an operating potential of4.5 V or more.

The core particles constituting the core portion of the present positiveelectrode active material particles may be, for example, a spinel-typelithium manganese-containing composite oxide which has a crystalstructure belonging to a space group Fd-3m, a lithiummanganese-containing composite oxide which has a layer structure, alithium manganese-containing composite oxide which has an olivinestructure, or a mixture of two or more kinds of these. The reason forthis is that the effect obtained by providing the layer A is believed tobe obtainable regardless of the composition of the core particles.

Among them, a 4 V-class spinel-type lithium manganese-containingcomposite oxide (also referred to as the “present 4 V-class spinel”)which has an operating potential of 3.5 V or more and less than 4.5 Vand a 5 V-class spinel-type lithium manganese-containing composite oxide(referred to as the “present 5 V-class spinel”) which has an operatingpotential of 4.5 V or more are particularly preferable from the effectof being able to improve the charge-discharge cycle ability and tosuppress the gas generation. Among them, the present 5 V-class spinel isparticularly preferable from the effect of being able to suppress gasgeneration.

Examples of the present 4 V-class spinel may include a powder (referredto as the “present 4 V-class spinel powder”) which contains spinel-typelithium manganese-containing composite oxide particles (referred to asthe “present 4 V-class spinel particles”) including a crystal phaseobtained by substituting a part of Mn sites in LiMn₂O_(4-δ) with a metalelement as the main component.

Examples of the present 5 V-class spinel may include a powder (referredto as the “present 5 V-class spinel powder”) which contains spinel-typelithium manganese-containing composite oxide particles (referred to asthe “present 5 V-class spinel particles”) including a crystal phaseobtained by substituting a part of Mn sites in LiMn₂O_(4-δ) with Li, ametal element M1, and another metal element M2 as the main component.

The metal element M1 is a substitution element which mainly contributesto the exertion of an operating potential of 4.5 V or more at the metalLi reference potential, examples thereof may include Ni, Co, and Fe, andas M1, another metal element may be contained as long as at least onekind of these are contained.

The metal element M2 is a substitution element which mainly contributesto the stabilization of the crystal structure leading to the enhancementof properties, examples of the substituent element which contributes toan improvement in capacity retention rate may include Mg, Ti, Al, Ba,Cr, Fe, Co, and Nb. As M2, another metal element may be contained aslong as at least one kind among these Mg, Ti, Al, Ba, Cr, Fe, Co, and Nbis contained.

As an example of the present 5 V-class spinel, a spinel-type lithiummanganese-containing composite oxide represented by Formula (1):Li[Li_(a)Mn_(2−a−c)M1_(b)M2_(c)] O_(4-δ) can be mentioned.

In Formula (1) above, “a” may be from 0.00 to 1.0 and it is even morepreferable that “a” is 0.01 or more or 0.5 or less among them and 0.02or more or 0.33 or less among them.

The “b” which indicates the content of M1 may be from 0.30 to 0.70, andit is even more preferable that “b” is 0.35 or more or 0.60 or lessamong them and 0.40 or more or 0.60 or less among them.

The “c” which indicates the content of M2 may be from 0.001 to 0.400,and it is even more preferable that “c” is 0.002 or more or 0.100 orless among them and 0.005 or more or 0.050 or less among them.

Incidentally, the “4-8” in each Formula above indicates that it may haveoxygen deficiency and a part of the oxygens may be substituted withfluorine.

However, the present 5 V-class spinel may contain other components aslong as the functions of Li, Mn, M1, M2 and O are not completelyinhibited. In particular, it may contain other elements as long as thecontent thereof is 0.5% by mass or less, respectively. This is becauseit is believed that the performance of the present spinel is not almostaffected in the amount to this extent.

(Layer A)

The layer A may contain at least titanium (Ti), aluminum (Al), zirconium(Zr), or two or more kinds of these.

The layer A may further contain phosphorus (P). Examples of the layer Acontaining phosphorus (P) may include the layer A containing Ti and P,the layer A containing Al and P, the layer A containing Zr and P, thelayer A containing Ti, Al, and P, the layer A containing Ti, Zr, and P,the layer A containing Al, Zr, and P, and the layer A containing Ti, Al,Zr, and P.

Incidentally, the layer A may contain other elements other than Ti, Al,Zr, P, and C.

In addition, the layer A has a feature that the content of carbon islow, and thus the content of carbon in the present positive electrodeactive material is preferably less than 0.1% by mass.

The content of carbon in the present positive electrode active materialis preferably less than 0.1% by mass, and it is preferably 0.09% by massor less among them and 0.08% by mass or less among them.

The layer A may be present so as to cover the entire surface of the coreparticle surface or it may be partially present on the core particlesurface so that there may be the part where the layer A is not present.

It is possible to suppress the reaction between the core particles andthe electrolytic solution and thus to suppress the gas generation as theentire surface or a part of the surface of the core particles isprovided with such a layer A. In addition, such a layer A also has thecharacteristic of not substantially affect the movement of a lithiumion.

Incidentally, another layer may be interposed between the core particlesurface and the layer A. For example, a layer containing an oxide oftitanium may be interposed.

In addition, another layer may be present on the surface side of thelayer A.

The thickness of the layer A is preferably from 0.1 to 200 nm from theviewpoint of enhancing the gas generation suppressing effect, and it ispreferably 0.2 nm or more or 190 nm or less among them and 0.3 nm ormore or 180 nm or less among them.

Such a layer A can be formed, for example, through a surface treatmentof the core particles. For example, it is possible to form the layer Aby conducting a surface treatment using a coupling agent which containstitanium (Ti), aluminum (Al), zirconium (Zr), or two or more kinds ofthese and then conducting a heat treatment at 300° C. or higher,preferably from 300 to 800° C., and preferably from 300 to 600° C. amongthem.

(D50)

In the present positive electrode active material, D50 according to avolume-based particle size distribution obtained by measuring by a laserdiffraction and scattering particle size distribution measuring methodis preferably from 3 to 40 μm, it is preferably 4 μm or more among themand 5 μm or more among them, and it is particularly preferably 10 μm ormore or 40 μm or less among them and 13 μm or more or 30 μm or lessamong them.

It is advantageous that D50 of the present positive electrode activematerial is from 3 to 40 μm and particularly from 5 to 40 μm from theviewpoint of the electrode fabrication.

In this manner, in order to adjust D50 of the present positive electrodeactive material to be in the above range, the calcining condition(temperature, time, atmosphere, and the like) or the strength ofcrushing (rotation number of crusher and the like) after calcination inthe production of the core particles may be adjusted. However, it is notlimited to these methods.

(D10)

In the present positive electrode active material, D10 according to avolume-based particle size distribution obtained by measuring by a laserdiffraction and scattering particle size distribution measuring methodis preferably from 1 to 20 μm, it is even more preferably 2 μm or moreamong them, 3 μm or more or 18 μm or less among them, and particularlypreferably 4 μm or more or 16 μm or less among them.

It is preferable that D10 of the present positive electrode activematerial is 1 μm or more and particularly 2 μm or more from theviewpoint that the slurry dispersibility at the time of coating theelectrode is more favorable and it is preferable that D10 is 16 μm orless from the viewpoint that it is possible to suppress a significantdecrease in viscosity of the slurry at the time of coating theelectrode.

In this manner, in order to adjust D10 of the present positive electrodeactive material to be in the above range, the calcining condition(temperature, time, atmosphere, and the like) or the strength ofcrushing (rotation number of crusher and the like) after calcination inthe production of the core particles may be adjusted. However, it is notlimited to these methods.

(Dmin)

In the present positive electrode active material, Dmin according to avolume-based particle size distribution obtained by measuring by a laserdiffraction and scattering particle size distribution measuring methodis preferably 10 μm or less, it is even more preferably 0.1 μm or moreamong them, 0.3 μm or more among them, and particularly preferably 0.5μm or more or 8 μm or less among them.

The fact that Dmin of the present positive electrode active material is10 μm or less means that the present positive electrode active materialcontains at least the present spinel particles having a particle size of10 μm and it is distinguished from those obtained by removing all thefine particles by classification.

In this manner, in order to adjust Dmin of the present positiveelectrode active material to be in the above range, the fine particlesattached to the surface of the present positive electrode activematerial particles may be removed using a difference in sedimentationvelocity as to be described later. However, it is not limited to thesemethods.

(Specific Surface Area)

The specific surface area (BET) of the present positive electrode activematerial is preferably from 0.01 to 3.00 m²/g, it is preferably 0.10m²/g or more or 2.00 m²/g or less among them, it is preferably 1.50 m²/gor less among them, it is particularly preferably 1.00 m²/g or lessamong them, and it is even more preferably 0.80 m²/g or less among them.

In general, it is a technical common sense that the reactivity with theelectrolytic solution increases and thus a gas is likely to be generatedas the specific surface area increases. However, the present spinelpowder is characterized in that it is possible to suppress the gasgeneration even though it has a specific surface area to the same extentas the conventional spinel-type lithium manganese-containing compositeoxide.

In this manner, in order to adjust the specific surface area of thepresent positive electrode active material to be in the above range, forexample, the temperature for the main calcination may be adjusted or thepresent positive electrode active material may be classified. However,it is not limited to these methods.

<Method for Producing Present Positive Electrode Active Material>

As a preferred example of the method for producing the present positiveelectrode active material, for example, it can be produced by aproduction method which includes a step of producing lithiummanganese-containing composite oxide particles (core particles), thenconducting a surface treatment using a mixture prepared by mixing asurface treatment agent such as a titanium coupling agent, an aluminumcoupling agent, a zirconium coupling agent, a titanium-aluminum couplingagent, or an aluminum-zirconium coupling agent with an organic solvent,and subsequently conducting a heat treatment.

(Method for Producing Present Spinel Powder)

As the method for producing lithium manganese-containing composite oxideparticles (core particles), a known method may be appropriatelyemployed.

Here, the method for fabricating a powder (referred to as the “presentspinel powder”) of the spinel-type lithium manganese-containingcomposite oxide having a crystal structure belonging to the space groupFd-3m will be described.

The present spinel powder can be obtained by mixing raw materials suchas a lithium compound, a manganese compound, an M1 metal compound, andan M2 metal compound, pulverizing using a wet pulverizer or the like,granulating and drying using a heat spray dryer or the like, calcining,conducting a heat treatment if necessary, and classifying if necessary.However, the method for producing the present spinel powder is notlimited to the production method. In particular, the production methodbefore introducing the spinel-type lithium manganese-containingcomposite oxide into water and stirring it is arbitrary. For example, agranulated powder to be subjected to calcination may be fabricated bythe so-called co-precipitation method, and the separating means aftercalcination may be changed to another method.

Examples of the lithium compound may include lithium hydroxide (LiOH),lithium carbonate (Li₂CO₃), lithium nitrate (LiNO₃), LiOH·H₂O, lithiumoxide (Li₂O), another fatty acid lithium, or a lithium halide. Amongthem, a hydroxide salt, a carbonate salt, and a nitrate salt of lithiumare preferable.

The manganese compound is not particularly limited. For example,manganese carbonate, manganese nitrate, manganese chloride, manganesedioxide, manganese trioxide, and trimanganese tetraoxide can be used,and manganese carbonate and manganese dioxide are preferable among them.Among them, electrolytic manganese dioxide obtained by electrolysis isparticularly preferable.

As the M1 metal compound and the M2 metal compound, a carbonate salt, anitrate salt, a chloride salt, an oxyhydroxide salt, a hydroxide and thelike of the M1 or M2 metal can be used.

Incidentally, a boron compound may be blended into the raw material. Theboron compound may be a compound containing boron (element B), and forexample, it is preferable to use boric acid or a lithium borate. Aslithium borate, it is possible to use various forms of lithium boratesuch as lithium metaborate (LiBO₂), lithium tetraborate (Li₂B₄O₇),lithium pentaborate (LiBO₈), and lithium perborate (Li₂B₂O₅).

A composite oxide phase containing Ni, Mn, and B, for example thecrystal phase Ni₅MnO₄(BO₃)₂ is formed in addition to the crystal phaseof the present spinel when such a boron compound is compounded.

As the method for mixing the raw materials, it is preferable to add aliquid medium such as water or a dispersant to the raw materials and toform a slurry by wet mixing them together, and it is preferable topulverize the slurry thus obtained using a wet pulverizer. However, itmay be dry pulverized.

The granulating method may be a dry method or a wet method as long asthe various kinds of raw materials which have been pulverized in theprevious step are not separated but are dispersed in the granulatedparticles, and it may be an extrusion granulation method, a tumblinggranulation method, a fluidized granulation method, a mixing granulationmethod, a spray drying granulation method, a pressure moldinggranulation method, or a flake granulation method using a roll or thelike. However, in the case of wet granulation, it is required tothoroughly dry the granulated particles before calcination. As thedrying method, the granulated particles may be dried by a known dryingmethod such as a spray thermal drying method, a hot air drying method, avacuum drying method, or a freeze-drying method, and among them, a spraythermal drying method is preferable. The spray thermal drying method ispreferably conducted using a thermal spray dryer (spray dryer).

It is preferable to conduct the calcination so that the granulatedparticles are held in a calcining furnace and an air atmosphere, anatmosphere having an adjusted oxygen partial pressure, or a carbondioxide gas atmosphere, or another atmosphere at a temperature of from800 to 1000° C. (it means the temperature in the case of bringing thethermocouple into contact with the material being calcined in thecalcining furnace) for from 0.5 to 300 hours. At this time, it ispreferable to select the calcining condition such that the transitionmetal converts into a solid solution at the atomic level to form asingle phase.

The kind of calcining furnace is not particularly limited. For example,it is possible to calcine the granulated particles using a rotary kiln,an electrostatic stationary furnace, and another calcining furnace.

It is preferable to conduct the heat treatment in the air atmosphere andan environment of from 500 to 800° C. and preferably 700° C. or higheror 800° C. or lower for from 0.5 to 300 hours so as to easilyincorporate oxygen into the granulated particles.

After the calcination or the heat treatment has been conducted in thismanner, the calcined particles are subjected to the crushing and theclassification if necessary, whereby the present spinel powder can beobtained.

Incidentally, it is possible to obtain the present spinel powder whichcan further suppress the gas generation by conducting a series ofseparation treatment that the present spinel powder obtained in thismanner is introduced into water, stirred by a stirring means such as astirrer, and then appropriately allowed to stand, the supernatant isremoved, and the precipitate is recovered at least one time andpreferably repeating it two or more times. Next, this separationtreatment will be described.

(Separation Treatment)

In the above separation treatment, it is preferable that the water inwhich the spinel-type lithium manganese-containing composite oxide(powder) is introduced has a pH of from 5 to 9, a temperature of from 15to 25° C., and a volume to be from 1.2 to 2 times to the spinel-typelithium manganese-containing composite oxide (powder).

It is also possible to use a liquid such as ethanol in addition towater.

The water tank to be filled with water preferably has a size of from 200to 5000 mL.

As the stirring means, it is possible to use an arbitrary stirring barsuch as a stirrer or a magnetic stirrer, and as the stirring speed, itis preferable to stir the powder to an extent to which the powder doesnot precipitate but flows and, as a guideline, for example, at arotational speed of from 200 to 250 rpm.

As the standing time after stirring, it is preferable to set anappropriate time for the state that most of the powder is settled andfine powders are suspended, and as a guideline, for example, it ispreferably from 1 to 5 minutes and particularly preferably 2 minutes orlonger or 3 minutes or shorter among them.

It is preferable to sufficiently remove hydrogen (H) in the vicinity ofthe surface, for example, by heating the recovered spinel-type lithiummanganese-containing composite oxide (powder) to 300° C. or higher.

(Method for Forming Layer A)

Next, the present spinel powder obtained as described above is subjectedto the surface treatment using a mixture prepared by mixing a surfacetreatment agent such as a titanium coupling agent or an aluminumcoupling agent or a zirconium coupling agent or a titanium-aluminumcoupling agent or an aluminum-zirconium coupling agent with an organicsolvent, dried to volatilize the organic solvent, and then subjected tothe heat treatment at 300° C. or higher to form the layer A, whereby itis possible to obtain the present positive electrode active material.

The coupling agent may be a compound having an organic functional groupand a hydrolyzable group in the molecule, and is preferably those whichhave phosphorus (P) in the side chain among them. A coupling agenthaving phosphorus (P) in the side chain exhibits more favorable affinityfor the binder and thus exhibits particularly excellent binding propertywith the binder.

In the case of conducting the surface treatment using such a couplingagent, it is required to dry the powder by heating, for example, to from40 to 120° C. in order to volatilize the organic solvent. Thereafter, itis preferable to heat at 300° C. or higher, particularly from 300 to800° C., and from 300 to 600° C. among them.

By heating the powder at 300° C. or higher in this manner, it ispossible to oxidize the layer A as well as to decrease the content ofcarbon in the layer A and it is possible to further enhance thecharge-discharge cycle ability depending on the kind of coupling agentin some cases.

The heat treatment after drying is preferably conducted in anoxygen-containing atmosphere. It is because there is a possibility thatoxygen in the active material is also lost at the same time as theorganic solvent or the side chain of the coupling agent is removed bythe heat treatment after drying, and thus it is preferable to replenishthe lost oxygen by conducting the heat treatment after drying in anoxygen-containing atmosphere. From this point of view, it is preferableto conduct the heat treatment after drying in an air atmosphere and anoxygen atmosphere among the oxygen-containing atmospheres.

Incidentally, the oxygen atmosphere indicates an atmosphere in which theabundance of oxygen is greater than in the air atmosphere.

<Application of Present Positive Electrode Active Material>

The present positive electrode active material can be effectivelyutilized as a positive electrode active material for various kinds oflithium batteries after being crushed and classified if necessary.

In the case of utilizing the present positive electrode active materialas a positive electrode active material for various kinds of lithiumbatteries, for example, it is possible to produce a positive electrodemixture by mixing the present positive electrode active material with aconductive material composed of carbon black or the like and a bindercomposed of the Teflon™ binder or the like. Thereafter, it is possibleto constitute a lithium battery using such a positive electrode mixtureas the positive electrode, a material, such as lithium or carbon, whichcan absorb and release lithium as the negative electrode, a solutionprepared by dissolving a lithium salt such as lithiumhexafluorophosphate (LiPF₆) in a mixed solvent such as ethylenecarbonate and dimethyl carbonate as the non-aqueous electrolyte.

The lithium battery constituted in this manner can be used, for example,in an electronic device such as a notebook computer, a mobile phone, acordless phone handset, a video movie, a liquid crystal television, anelectric shaver, a portable radio, a headphone stereo, a backup powersupply, or a memory card, a medical device such as a pacemaker or ahearing aid, a driving power source for being mounted in an electricvehicle. Among them, it is particularly effective as various kinds ofportable computers requiring excellent cycle characteristics such as amobile phone, a PDA (portable information terminal), and a notebookcomputer, a driving power source of an electric vehicle (including ahybrid car) or a power source for power storage.

<Description of Phrase>

In the present specification, in a case in which it is expressed as “Xto Y” (X and Y are arbitrary numbers), it also includes the meaning of“preferably more than X” or “preferably less than Y” as well as themeaning of “X or more and Y or less” unless otherwise stated.

In addition, in a case in which it is expressed as “X or more” (X is anarbitrary number) or “Y or less” (Y is an arbitrary number), it is alsoinclude the intention to instruct “preferable to be more than X” or“preferable to be less than Y”.

In addition, each of the numerical value ranges specified in theinvention is intended to include the range that falls within a range ofthe upper limit value and the lower limit value when being rounded offunless otherwise stated. However, it is preferably within the range ofthe numerical value obtained by truncating the figure below thesignificant figure.

EXAMPLES

Next, the invention will be further described based on Examples andComparative Examples. However, the invention is not limited to Examplesto be described below. The condition for the surface treatment ispresented in Table 1.

Comparative Example 1

Lithium carbonate, electrolytic manganese dioxide, nickel hydroxide,titanium oxide, and lithium tetraborate (Li₂B₄O₇) were weighed so as tobe Li: 3.9% by mass, Mn: 40.1% by mass, Ni: 15.5% by mass, Ti: 5.3% bymass, and B: 0.14% by mass, mixed together by adding water, and stirredto prepare a slurry having a solid concentration of 10 wt %.

Ammonium polycarboxylate (SN-DISPERSANT 5468 manufactured by SAN NOPCOLIMITED) as the dispersant was added to the slurry (raw material powder:500 g) thus obtained in an amount of being 6 wt % of solid content ofthe slurry, and the slurry was pulverized at 1300 rpm for 20 minutesusing a wet pulverizer so as to have an average particle size (D50) of0.5 μm or less.

The pulverized slurry thus obtained was granulated and dried using athermal spray dryer (spray dryer “i-8” manufactured by OHKAWARA KAKOHKICO., LTD.). At this time, a rotating disc was used for spraying, and thegranulation and drying was conducted at a rotation number of 24000 rpmand a supply amount of the slurry of 12 kg/hr by adjusting thetemperature such that the exit temperature of the drying tower was 100°C.

The granulated powder thus obtained was calcined at 950° C. for 70 hoursin the air using a stationary electric furnace and then subjected to theheat treatment at 700° C. for 70 hours in the air. The calcined powderobtained by heat treatment was classified using a sieve having a mesh of75 μm, and the undersize particles were recovered, thereby obtaining aspinel-type lithium manganese-containing composite oxide powder.

The spinel-type lithium manganese-containing composite oxide powder thusobtained was identified using an X-ray diffraction apparatus (XRD), andthe result demonstrated that it was a 5 V-class spinel-type lithiummanganese-containing composite oxide represented by Formula (1): Li[Li_(a)Mn_(2−a−c)M1_(b)M2_(c)] O_(4-δ).

Into a plastic beaker with handles (volume: 2000 mL) which was filledwith water having a pH of from 6 to 7, a temperature of 20° C., and avolume of 2000 mL, 1 kg of the spinel-type lithium manganese-containingcomposite oxide powder thus obtained was introduced and stirred at arotation speed of from 200 to 250 rpm for 10 minutes using a stirrer(propeller area: 24 cm²), stirring was then stopped, the stirrer takenout from the water, and the resultant was allowed to stand for 2minutes. Thereafter, the supernatant up to the height of 5/12 wasremoved through decantation, the residual was recovered as a precipitateusing a suction filtration machine (filter paper: 131), the precipitatethus recovered was allowed to stand for 24 hours in an environment of120° C. to dry it and then further allowed to stand for 24 hours in astate of being heated so as to have the product temperature of 500° C.to dry it.

Example 1

Using a cutter mill (MILLSER 720G manufactured by Iwatani Corporation),100 parts by mass of the spinel-type lithium manganese-containingcomposite oxide powder obtained in the same manner as in ComparativeExample 1, 1.0 part by mass of a titanium coupling agent (PLENACT™KR-46B manufactured by Ajinomoto Fine-Techno Co., Inc.) as the surfacetreatment agent, and 1.4 parts by mass of isopropyl alcohol as thesolvent were mixed together. Subsequently, the mixed spinel-type lithiummanganese-containing composite oxide powder was dried by placing in adryer under the conditions of 100° C. and 1 hour in the air and thenheated such that a state of having the product temperature of 500° C.was maintained for 5 hours, thereby obtaining a spinel-type lithiummanganese-containing composite oxide powder (sample) with asurface-treated layer.

The cross section in the vicinity of the particle surface of thespinel-type lithium manganese-containing composite oxide powder (sample)fabricated in this manner was observed using a transmission electronmicroscope (“JEM-ARM200F” manufactured by JEOL Ltd.), and the resultdemonstrated that the layer A was partially present on the surface ofthe core portion composed of the spinel-type lithiummanganese-containing composite oxide. In addition, the layer A wasanalyzed by EDS, and it was found to contain titanium (Ti) andphosphorus (P). The thickness of the layer A was different depending onthe location, and the thin part was 0.1 nm and the thick part was 50 nm.

Example 2

A spinel-type lithium manganese-containing composite oxide powder(sample) with a surface-treated layer was obtained by the same method asin Example 1 except that the surface treatment agent used in Example 1was changed to an aluminum coupling agent (PLENACT™ AL-M manufactured byAjinomoto Fine-Techno Co., Inc.).

The cross section in the vicinity of the particle surface of thespinel-type lithium manganese-containing composite oxide powder (sample)fabricated in this manner was observed using a transmission electronmicroscope (“JEM-ARM200F” manufactured by JEOL Ltd.), and the resultdemonstrated that the layer A was partially present on the surface ofthe core portion composed of the spinel-type lithiummanganese-containing composite oxide. In addition, the layer A wasanalyzed by EDS, and it was found to contain aluminum (Al). Thethickness of the layer A was different depending on the location, andthe thin part was 0.1 nm and the thick part was 40 nm.

Example 3

A spinel-type lithium manganese-containing composite oxide powder wasobtained in the same manner as in Comparative Example 1 except that thecalcination temperature of 950° C. in Comparative Example 1 was changedto 880° C. Thereafter, a spinel-type lithium manganese-containingcomposite oxide powder (sample) with a surface-treated layer wasobtained by subjecting this spinel-type lithium manganese-containingcomposite oxide powder to the surface treatment, drying, and heattreatment in the same manner as in Example 1.

The cross section in the vicinity of the particle surface of thespinel-type lithium manganese-containing composite oxide powder (sample)fabricated in this manner was observed using a transmission electronmicroscope (“JEM-ARM200F” manufactured by JEOL Ltd.), and the resultdemonstrated that the layer A was partially present on the surface ofthe core portion composed of the spinel-type lithiummanganese-containing composite oxide. In addition, the layer A wasanalyzed by EDS, and it was found to contain titanium (Ti) andphosphorus (P). The thickness of the layer A was different depending onthe location, and the thin part was 0.1 nm and the thick part was 20 nm.

Comparative Example 2

A spinel-type lithium manganese-containing composite oxide powder wasobtained in the same manner as in Comparative Example 1 except thatlithium carbonate, electrolytic manganese dioxide, nickel hydroxide,titanium oxide, and lithium tetraborate (Li₂B4O₇) were weighed so as tobe Li: 3.9% by mass, Mn: 42.3% by mass, Ni: 14.3% by mass, Ti: 3.8% bymass, and B: 0.14% by mass and mixed together.

Example 4

A spinel-type lithium manganese-containing composite oxide powder wasobtained in the same manner as in Comparative Example 2. Thereafter, aspinel-type lithium manganese-containing composite oxide powder (sample)with a surface-treated layer was obtained by subjecting this spinel-typelithium manganese-containing composite oxide powder to the surfacetreatment presented in Table 1.

The cross section in the vicinity of the particle surface of thespinel-type lithium manganese-containing composite oxide powder (sample)fabricated in this manner was observed using a transmission electronmicroscope (“JEM-ARM200F” manufactured by JEOL Ltd.), and the resultdemonstrated that the layer A was partially present on the surface ofthe core portion composed of the spinel-type lithiummanganese-containing composite oxide. In addition, the layer A wasanalyzed by EDS, and it was found to contain aluminum (Al). Thethickness of the layer A was different depending on the location, andthe thin part was 0.1 nm and the thick part was 30 nm.

Example 5

A spinel-type lithium manganese-containing composite oxide powder wasobtained in the same manner as in Comparative Example 2. Thereafter, aspinel-type lithium manganese-containing composite oxide powder (sample)with a surface-treated layer was obtained by subjecting this spinel-typelithium manganese-containing composite oxide powder to the surfacetreatment presented in Table 1.

The cross section in the vicinity of the particle surface of thespinel-type lithium manganese-containing composite oxide powder (sample)fabricated in this manner was observed using a transmission electronmicroscope (“JEM-ARM200F” manufactured by JEOL Ltd.), and the resultdemonstrated that the layer A was partially present on the surface ofthe core portion composed of the spinel-type lithiummanganese-containing composite oxide. In addition, the layer A wasanalyzed by EDS, and it was found to contain titanium (Ti) andphosphorus (P). The thickness of the layer A was different depending onthe location, and the thin part was 0.1 nm and the thick part was 20 nm.

Example 6

A spinel-type lithium manganese-containing composite oxide powder wasobtained in the same manner as in Comparative Example 2. Thereafter, aspinel-type lithium manganese-containing composite oxide powder (sample)with a surface-treated layer was obtained by subjecting this spinel-typelithium manganese-containing composite oxide powder to the surfacetreatment presented in Table 1. A zirconium coupling agent (Ken-React™NZ12 manufactured by Kenrich Petrochemicals, Inc.) was used as thesurface treatment agent.

The cross section in the vicinity of the particle surface of thespinel-type lithium manganese-containing composite oxide powder (sample)fabricated in this manner was observed using a transmission electronmicroscope (“JEM-ARM200F” manufactured by JEOL Ltd.), and the resultdemonstrated that the layer A was partially present on the surface ofthe core portion composed of the spinel-type lithiummanganese-containing composite oxide. In addition, the layer A wasanalyzed by EDS, and it was found to contain Zr (zirconium) and P(phosphorus). The thickness of the layer A was different depending onthe location, and the thin part was 0.1 nm and the thick part was 90 nm.

<Method for Measuring Various Physical Property Values>

Various kinds of physical property values of the spinel-type lithiummanganese-containing composite oxide powders (samples) obtained inExamples and Comparative Examples were measured as follows.

(Specific Surface Area)

The specific surface area (BET) of the spinel-type lithiummanganese-containing composite oxide powders (samples) obtained inExamples and Comparative Examples was measured as follows.

First, 0.5 g of the sample (powder) was weighed and introduced into theglass cell for a flow system gas adsorption method specific surface areameasuring apparatus MONOSORB LOOP (“product name: MS-18” manufactured byYuasa Ionics Co., Ltd.), the inside of the glass cell was purged with anitrogen gas at a gas flow rate of 30 mL/min using a pretreatmentapparatus for the MONOSORB LOOP for 5 minutes, and then subjected to theheat treatment at 250° C. for 10 minutes in the nitrogen gas atmosphere.Thereafter, the sample (powder) was subjected to the measurement by BETequation one point method using the MONOSORB LOOP.

Incidentally, a mixed gas of 30% nitrogen : 70% helium was used as theadsorption gas at the time of the measurement.

(D10, D50, and Dmin)

For the spinel-type lithium manganese-containing composite oxide powders(samples) obtained in Examples and

Comparative Examples, the sample (powder) was introduced into awater-soluble solvent and irradiated with ultrasonic waves of 40 W at aflow rate of 40% for 360 seconds using an automatic sample supplymachine for laser diffraction particle size distribution measuringapparatus (“Microtorac SDC” manufactured by NIKKISO CO., LTD.), theparticle size distribution was then measured using a laser diffractionparticle size distribution measuring apparatus “MT3000II” manufacturedby NIKKISO CO., LTD., and D10, D50, and Dmin were determined from thevolume-based particle size distribution chart thus obtained,respectively.

Incidentally, the water-soluble solvent used in the measurement wasfiltered through a filter of 60 w, the measurement was conducted twotimes by setting the solvent refractive index to 1.33, the particlepenetration condition to penetration, the particle refractive index to2.46, the shape to a non-spherical shape, the measurement range to from0.133 to 704.0 μm, and the measurement time to 30 seconds, and anaverage value thereof was adopted as D10, D50, Dmin, respectively.

(Measurement of Content of Carbon)

The spinel-type lithium manganese-containing composite oxide powders(samples) obtained in Examples and Comparative Examples were subjectedto measurement of the content of carbon (“C content” in Table 3). Theanalyzer and the measurement condition are as follows.

-   -   Analyzer: analyzer for carbon in solid (EMIA-110 manufactured by        HORIBA, Ltd.)    -   Carrier gas: oxygen (purity: 99.95% or more), gas pressure:        0.75±0.05 kgf/cm² and    -   Measurement condition: standard setting condition described in        manual for EMIA-110 (combustion set time was changed to 60        seconds)

(Measurement of Components)

The content of lithium, the content of manganese, the content of nickel,the content of titanium, the content of aluminum, and the content ofzirconium in the spinel-type lithium manganese-containing compositeoxide powders (samples) obtained in Examples 1, 4, 6 and ComparativeExamples 1 and 2 were measured by inductive coupling plasma (ICP)emission spectroscopic analysis, and the results are presented in Table2.

<Evaluation of Battery>

Laminate-type batteries were fabricated using the spinel-type lithiummanganese-containing composite oxide powders (samples) fabricated inExamples and Comparative Examples as the positive electrode activematerial and subjected to the gas generation evaluation test, and2032-type coin cell batteries were fabricated and subjected to thehigh-temperature cycle evaluation test.

(Fabrication of Laminate-Type Battery)

A mixture of 89 wt % of the spinel-type lithium manganese-containingcomposite oxide powders (samples) fabricated in Examples and ComparativeExamples, 5 wt % of acetylene black as the conductive auxiliary agent,and 6 wt % of PVDF as the binder was adjusted into a paste form byadding NMP (N-methylpyrrolidone). This paste was coated on an Al foilcurrent collector having a thickness of 15 μm and dried at 120° C.Thereafter, the coated Al foil current collector was pressed so as tohave a thickness of 80 μm, thereby fabricating the positive electrodesheet.

A copper foil having a thickness of 18 μm was used as the negativeelectrode current collector. The mixture of 92 wt % of graphite as theactive material and 8 wt % of PVDF as the binder material was preparedin a paste form by adding NMP. This paste was uniformly coated on thenegative electrode current collector and dried at 100° C. Thereafter,the coated negative electrode current collector was pressed so as tohave a thickness of 80 μm, thereby fabricating the negative electrodesheet.

The positive electrode sheet thus obtained was cut into a size of 2.9cm×4.0 cm to use as the positive electrode, meanwhile, the negativeelectrode sheet thus obtained was cut into a size of 3.1 cm×4.2 cm touse as the negative electrode, and a separator (porous polyethylenefilm) that was impregnated with an electrolytic solution prepared bydissolving LiPF₆ in a mixed solvent of ethylene carbonate, ethyl methylcarbonate, and dimethyl carbonate (volume ratio=20:20:60) so as to be 1mol/L and further adding vinylene carbonate as the additive at 2% byvolume was sandwiched between the positive electrode and the negativeelectrode, thereby fabricating a laminate-type battery.

(Gas Generation Evaluation Test)

The laminate-type battery fabricated by the method described above wasleft to stand for 12 hours, then charged at a current density of 0.2mA/cm² and a measurement environment of 25° C. until a difference inpotential between both electrodes became 4.9 V, thereafter, dischargedat 0.2 mA/cm² until a difference in potential became 3.0 V. Thereafter,the measurement environment temperature was set to 45° C., and thelaminate-type battery was left to stand for 4 hours, charged at the samecurrent value as above until a difference in potential between bothelectrodes became 4.9 V, maintained at that voltage for 7 days, and thendischarged to 3.0 V.

The quantity (mL) of gas generated so far was measured by a dippingvolumetric method (solvent substitution method based on Archimedes'principle).

Incidentally, the result in Table 3 indicates one that was calculatedfrom the average value of the numerical values measured for each of twolaminate-type batteries, and the quantity of gas generated in therespective Examples was presented as the relative value (%) with respectto 100% of the quantity of gas generated in Comparative Example 1.

(Fabrication of 2032-Type Coin Cell Battery)

The positive electrode sheet thus obtained was cut into a size of φ 13to use as the positive electrode, meanwhile, the negative electrodesheet thus obtained was cut into a size of φ 14 to use as the negativeelectrode, and a separator (porous polyethylene film) that wasimpregnated with an electrolytic solution prepared by dissolving LiPF₆in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, anddimethyl carbonate (volume ratio=20:20:60) so as to be 1 mol/L andfurther adding vinylene carbonate as the additive at 2% by volume wassandwitched between the positive electrode and the negative electrode,thereby fabricating a 2032-type coin cell battery.

(High-Temperature Cycle Evaluation Test)

These 2032-type coin cell batteries were charged to 4.9 V and dischargedto 3.0 V at normal temperature, and this was repeated three cycles toconduct initial activation.

Thereafter, these 2032-type coin cell batteries were subjected to thecharge and discharge cycle test at 0.5 C in an environment of 45° C.

As an indicator of the cycle test, the number of cycles at which thedischarge capacity reached 70% with respect to 100% of the referencethat was the capacity in the third cycle of the cycle test in anenvironment of 45° C. was used, and the number of cycles is presented inTable 3.

TABLE 1 Condition for surface treatment Coupling agent Solvent AmountAmount added added Drying Heat treatment (parts by (parts by TemperatureTemperature Kind mass) Kind mass) Atmosphere (° C.) Atmosphere (° C.)Example 1 Ti 1.0 Isopropyl 1.4 In air 100 In air 500 Example 2 Alalcohol atmosphere atmosphere Example 3 Ti Example 4 Al 3.0 4.2 *Inoxygen Example 5 Ti atmosphere Example 6 Zr *The treatment was conductedby setting the flow rate of oxygen to 0.5 mL/min in order to obtain theoxygen atmosphere.

TABLE 2 Analysis value (wt. %) Li Mn Ni Ti Al Zr Example 1 3.97 39.315.5 5.10 <0.01 <0.01 Example 4 3.94 40.2 13.8 3.63 0.16 <0.01 Example 63.91 40.6 14.3 3.63 <0.01 0.027 Comparative 4.10 39.6 15.9 4.98 <0.01<0.01 Example 1 Comparative 3.94 40.7 14.2 3.67 <0.01 <0.01 Example 2

TABLE 3 Result of particle Number of cycles having discharge sizedistribution capacity retention rate of 70% with measurement Quantity ofgas respect to capacity of third D50 D10 Dmin C content BET (ComparativeExample 1 high-temperature cycle (capacity μm μm μm % by mass m²/g isset to 100%) of third cycle is set to 100%) Example 1 24.5 15.3 6.00.004 0.22 80 277 Example 2 26.0 14.4 6.0 0.01 0.20 90 250 Example 317.0 10.4 4.2 0.004 0.35 55 293 Example 4 16.4 7.2 1.5 0.004 0.78 20 253Example 5 16.9 7.3 2.5 0.002 0.35 20 340 Example 6 16.8 7.4 2.5 0.0250.35 20 300 Comparative 25.7 13.3 5.0 0.004 0.15 100 235 Example 1Comparative 16.2 6.2 1.5 0.004 0.25 60 235 Example 2

(Discussion)

From the results above, it has been found that according to a lithiummanganese-containing composite oxide powder in which the entire surfaceor a part of the core particle surface is equipped with the layer Acontaining at least titanium (Ti), aluminum (Al), zirconium (Zr), or twoor more of these as described above, it is possible to improve thecharge-discharge cycle ability, moreover it is possible to effectivelysuppress the quantity of gas generated by reaction with the electrolyticsolution. It is believed that this is because the layer A is selectivelyformed at the active spots on the core particle surface. Incidentally,the presence of the layer A has been confirmed even using an X-rayphotoelectron spectroscopic (XPS) analyzer.

Furthermore, it is possible to confirm a change in composition derivedfrom the coupling agent component when Example 1 and Comparative Example1 and Examples 4 and 6 and Comparative Example 2 are compared in Table2. It indicates that the layer A is formed on the entire surface or apart of the core particle surface together with the results of analysisby EDS.

In addition, it has been found that the quantity of gas generated isfurther decreased in Examples 4, 5, and 6 in which the heat treatmentwas conducted in an oxygen-containing atmosphere. It is possible topresume that this is because the loss of oxygen from the positiveelectrode active material at the time of the heat treatment issuppressed by the supply of oxygen in the atmosphere.

1. A positive electrode active material for a lithium secondary batterycomprising positive electrode active material particles, wherein thepositive electrode active material particles comprises a layer (referredto as the “layer A”) comprising at least titanium (Ti), aluminum (Al),zirconium (Zr), or two or more kinds of these on the entire surface or apart of surface of lithium manganese-containing composite oxideparticles (also referred to as the “core particles”) operating at acharging voltage in a region exceeding 4.3 V in a metal Li referencepotential.
 2. A positive electrode active material for a lithiumsecondary battery comprising positive electrode active materialparticles, wherein the positive electrode active material particlescomprises a layer (referred to as the “layer A”) comprising at leasttitanium (Ti), aluminum (Al), or both of these on the entire surface ora part of surface of lithium manganese-containing composite oxideparticles (also referred to as the “core particles”) operating at acharging voltage in a region exceeding 4.3 V in a metal Li referencepotential.
 3. The positive electrode) active material for a lithiumsecondary battery according to claim 1, wherein a content of carbon (C)is less than 0.1% by mass.
 4. The positive electrode active material fora lithium secondary battery according to claim 1, wherein the layer Afurther comprises phosphorus (P).
 5. The positive electrode activematerial for a lithium secondary battery according to claim 1, wherein athickness of the layer A is from 0.1 to 200 nm.
 6. The positiveelectrode active material for a lithium secondary battery according toclaim 1, wherein the positive electrode active material has a specificsurface area of from 0.01 to 3.00 m²/g.
 7. The positive electrode activematerial for a lithium secondary battery according to claim 1, whereinD50 according to a volume-based particle size distribution obtained bymeasuring by a laser diffraction and scattering particle sizedistribution measuring method is from 3 to 40 μm.
 8. The positiveelectrode active material for a lithium secondary battery according toclaim 1, wherein D10 according to a volume-based particle sizedistribution obtained by measuring by a laser diffraction and scatteringparticle size distribution measuring method is from 1 to 20 μm.
 9. Thepositive electrode active material for a lithium secondary batteryaccording to claim 1, wherein Dmin according to a volume-based particlesize distribution obtained by measuring by a laser diffraction andscattering particle size distribution measuring method is 10 μm or less.10. The positive electrode active material for a lithium secondarybattery according to claim 1, wherein the lithium manganese-containingcomposite oxide particles are spinel-type lithium manganese-containingcomposite oxide particles having an operating potential of 4.5 V or moreat a metal Li reference potential.
 11. The positive electrode activematerial for a lithium secondary battery according to claim 1, whereinthe lithium manganese-containing composite oxide particles arespinel-type lithium manganese-containing composite oxide particlesincluding a crystal phase obtained by substituting a part of Mn sites inLiMn₂O_(4-δ) with Li, a metal element M1, and another metal element M2.12. A lithium secondary battery comprising the positive electrode activematerial for a lithium secondary battery according to claim
 1. 13. Thepositive electrode active material for a lithium secondary batteryaccording to claim 2, wherein a content of carbon (C) is less than 0.1%by mass.
 14. The positive electrode active material for a lithiumsecondary battery according to claim 2, wherein the layer A furthercomprises phosphorus (P).
 15. The positive electrode active material fora lithium secondary battery according to claim 2, wherein a thickness ofthe layer A is from 0.1 to 200 nm.
 16. The positive electrode activematerial for a lithium secondary battery according to claim 2, whereinthe positive electrode active material has a specific surface area offrom 0.01 to 3.00 m²/g.
 17. The positive electrode active material for alithium secondary battery according to claim 2, wherein D50 according toa volume-based particle size distribution obtained by measuring by alaser diffraction and scattering particle size distribution measuringmethod is from 3 to 40 μm.
 18. The positive electrode active materialfor a lithium secondary battery according to claim 2, wherein D10according to a volume-based particle size distribution obtained bymeasuring by a laser diffraction and scattering particle sizedistribution measuring method is from 1 to 20 μm.
 19. The positiveelectrode active material for a lithium secondary battery according toclaim 2, wherein Dmin according to a volume-based particle sizedistribution obtained by measuring by a laser diffraction and scatteringparticle size distribution measuring method is 10 μm or less.
 20. Thepositive electrode active material for a lithium secondary batteryaccording to claim 2, wherein the lithium manganese-containing compositeoxide particles are spinel-type lithium manganese-containing compositeoxide particles having an operating potential of 4.5 V or more at ametal Li reference potential.